A variety of devices are known that include radio frequency (RF) transmitters, or transceivers, for communicating with other compatible devices. Examples of such devices include radiotelephones (which may be cordless or cellular telephones), two-way radios, modems, smart phones, personal digital assistants (PDA), or the like. Those devices that operate in two modes are called dual mode devices. Dual mode devices transmit signals according to two different formats, such as digital time division multiple access (TDMA) and analog signaling formats. Other devices operate in two frequency bands, and are referred to as dual band. For example, digital TDMA devices operate at 900 MHz and 1800 MHz.
It is known to provide separate amplifiers for dual mode devices. In such circuits, switches are used to select one amplifier for one mode and another independent amplifier for the other mode. Although this arrangement provides for optimum performance in each mode, it requires two independent amplifiers, which is costly. Additionally, the switches used to select the amplifier for a particular mode add harmonic noise to the system.
Dual mode devices are also known which incorporate a single, multi-stage amplifier having interstage switchable matching networks for accommodating both modes of operation. However, these systems are inefficient when applied to dual band devices.
Accordingly, there is a need for a more efficient, and improved, amplifier system for dual band devices.